The present invention relates generally to transmissions for use in motor vehicles and, more particularly, to a twin-clutch automated transmission applicable for use in rear-wheel drive vehicles.
Automobile manufacturers continuously strive to improve fuel efficiency. This effort to improve fuel efficiency, however, is typically offset by the need to provide enhanced comfort and convenience to the vehicle operator. For example, it is well known that manual transmissions are more fuel efficient than automatic transmissions, yet a majority of all passenger vehicles are equipped with automatic transmissions due to the increased convenience they provide.
More recently, xe2x80x9cautomatedxe2x80x9d variants of conventional manual transmissions have been developed which shift automatically without any input from the vehicle operator. Such automated transmissions typically include a plurality of power-operated actuators that are controlled by a transmission controller to shift traditional synchronized dog clutches. However, such automated transmissions have the disadvantage that there is a power interruption in the drive connection between the input shaft and the output shaft during sequential gear shifting. Power interrupted shifting results in a harsh shift feel which is generally considered to be unacceptable when compared to smooth shift feel associated with most automatic transmissions. To overcome this problem, automated twin-clutch transmissions have been developed which can be powershifted to permit gearshifts to be made under load. Examples of such automated manual transmissions are shown in U.S. Pat. Nos. 5,966,989 and 5,890,392. While such powershift twin-clutch transmissions overcome several drawbacks associated with conventional single-clutch automated transmissions, a need exists to develop simpler and more robust transmissions which advance the automotive transmission technology.
Accordingly, it is an object of the present invention to provide an automated powershift transmission and a control system for permitting automatic shifting of the transmission.
This and other objects of the present invention are met by providing an automated powershift multi-speed transmission adapted to transfer power from the engine to the driveline of a motor vehicle. The transmission includes an engine clutch assembly having a primary clutch operable to establish a releasable drive connection between the engine and a first input shaft, and a secondary clutch operable to establish a releasable drive connection between the engine and a second input shaft. The transmission also includes an output shaft adapted to transfer power to the driveline, and a geartrain for selectively establishing a plurality of forward and reverse speed ratio drive connections between the input shafts and the output shaft. In addition, the transmission includes power-operated dog clutches for selectively engaging constant-mesh gearsets associated with the geartrain, and a transmission controller for controlling coordinated actuation of the engine clutch assembly and the power-operated dog clutches to permit non-power interrupted (xe2x80x9cpowershiftxe2x80x9d) sequential gear changes automatically without input from the vehicle operator. A clutch control system includes a first hydraulic pump driven by the first input shaft, a second hydraulic pump driven by the second input shaft, and flow control valving for controlling fluid flow between the first and second pumps. When shifting under power between gear ratios, one of the clutches associated with the engine clutch assembly is released such that the pump associated with the driven input shaft supplies fluid to the pump associated with released input shaft for causing acceleration/deceleration of the released input shaft into synchronization with the output shaft. Following completion of speed synchronization, the dog clutch for the selected gearset associated with the released input shaft is actuated and thereafter the released clutch is re-engaged and the engaged clutch is released.
In accordance with an alternative arrangement, the clutch control system can include a single control valve in combination with the engine clutch assembly operable for selectively establishing drive connections between the engine and each of the first and second input shafts.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the scope of this invention will become apparent to those skilled in the art.